The present invention relates to an aircraft navigational and landing system, and more particularly to a Local Area Augmentation System.
A Local Area Augmentation System (LAAS) is Global Positioning System (GPS) Landing System (GLS) used at some airports as a primary or auxiliary landing system for certain runways. The system comprises a ground-based radio receiver that receives signals from a plurality of satellites of the Global Positioning System. The GLS also has available a transmitter that is used to communicate certain navigation and landing information to aircraft wishing to avail themselves of the GLS as an aid to landing on the runway to which the GLS is dedicated.
It is possible that one or more of the satellites of the Global Positioning System may fail. In addition, the GPS is operated under the control of the U.S. Government, which can modify the accuracy of the GPS in the event of, for example, the use of the GPS by enemy aircraft or missiles. Thus the ground-based GPS receiver continually monitors the satellites for failure or inaccuracy and relates that information as well as navigation and landing information to the aircraft.
Since the GPS receiver of the LAAS system is in a fixed and known position, the actual position of the receiver antenna is continually compared to the information being received by the LAAS GPS receiver. Any disparity between the actual position of the receiving antenna and the information provided by the GPS satellites is included in an error correction factor which is transmitted to any aircraft using the LAAS GLS. Also, since the position of the end of the runway which the GLS is serving is also fixed and known, any error factors would also be applicable to the signals identifying the approach end of the runway to the aircraft.
In addition to the navigation and landing information carried on the digital uplink from the ground-based transmitter, LAAS systems additionally transmit to the aircraft identification signals providing ground station frequency and runway identification information that the pilot (or crewmember) of the aircraft can use to confirm that the transmission being received is for the runway and airport at which it is desired to land.
Presently, GLS systems do not provide the pilot of an aircraft utilizing the system with an indication of distance to the end of the runway. ILS systems, in addition to a glide slope signal, provide marker beacons that signal to the pilot certain distances or positions with respect to the end of the runway which the aircraft is approaching. Typically, three beacons are provided, an outer marker, a middle marker, and an inner marker. Each of the beacons is identified by a visual indicator (typically a light of the instrument panel) and an aural indicator (typically a Morse code identifier of the identity of the beacon). Consequently, it would be useful to provide to the users of a GLS system a similar signaling mechanism that would alert the aircraft pilot of the position of the aircraft with respect to the approach end of the runway.
A system for providing distance information to the pilot of an aircraft utilizing a GPS Landing System (GLS) Local Area Augmentation System (LAAS) as a navigation and landing aid for the aircraft is provided, which includes a radio receiver adapted to receive signals from a ground-based radio transmitter associated with the LAAS, the signals including signals representing the location of the LAAS. A Global Positioning System (GPS) receiver adapted to receive position signals from GPS satellites and for producing signal representing the location of the aircraft is also provided, as is a controller coupled to the radio receiver and to the GPS receiver for receiving the signals representing the locations of the LAAS and of the aircraft, respectively, and for calculating the distance of the aircraft from the LAAS. A signaling mechanism coupled to the controller provides to the pilot of the aircraft with information representing the distance of the aircraft to the end of the runway.